What value should come in place of the question mark (?) in the following question?

52x14+145018=1998÷?

If x+1x=5, then the value of 6xx2+x+1 is,

If a > b > 0, AB = a - b cm, BC = 2√ab cm, then ∠ABC is

PR is a tangent to a circle with centre O and radius 4 cm at point Q. If ∠POR = 90°, OR = 5 cm and OP = 20/3 cm, then the length of PR is:

From a point, 40 m apart from the foot of a tower, the angle of elevation of its top is 60°. The height of the tower is

The radius of a sphere and hemisphere are same. The ratio of their total surface area is

Two equal arcs of two circles subtend angle of  60° and 75° at the centre. The ratio of the radii of the two circles is

If x + (1/x) = 2, then what is the value of x64 + x121?

If the diameter of a sphere is 14 cm, then what is the surface area (in sq.cm) of the sphere?